1. Field of the Invention
Embodiments of the invention relate to a flow indicator and an apparatus for monitoring particles in air. More particularly, embodiments of the invention relate to an apparatus adapted to draw an air sample from the air in a clean room and count particles contained in the air sample, and a flow indicator adapted to indicate the flow rate of the air sample.
This application claims priority to Korean Patent Application No. 10-2005-0044890, filed on May 27, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
Semiconductor devices are commonly manufactured by performing a complex sequence of fabrication processes that form a number of semiconductor dies, i.e., a number of electrical circuits individually formed on portions of a silicon wafer used as a substrate. Once the semiconductor dies have been formed on a silicon wafer an electrical die sorting (EDS) process is performed which inspects the electrical characteristics of the electrical circuits formed by the sequence of fabrication processes. Thereafter, individual semiconductor dies are removed from the silicon wafer and packaged to form a competed semiconductor device. This packaging process generally involves encapsulating each semiconductor die in an epoxy resin.
The sequence of fabrication processes usually includes one or more of: a deposition process adapted to deposit a material layer on the substrate; a chemical mechanical polishing (CMP) process adapted to planarize a material layer; a photolithography process adapted to form a photoresist pattern, an etching process adapted to form a pattern having desired electrical characteristics from a material layer using the photoresist pattern; an ion implantation process adapted to selectively implant ions into specific regions of the substrate; a cleaning process adapted to remove impurities from the substrate; a drying process adapted to dry cleaned substrate; an inspection process adapted to identify defects in the material layer and/or the pattern; etc.
Many if not all of these fabrication processes are performed in a conventional clean room. Clean rooms are widely used to prevent workpieces, such as silicon wafers, from becoming contaminated by particles in the air such as ordinary dust. The carefully controlled environment of a clean room is managed in accordance with various defined classes of cleanliness. Each clean room class is defined by the concentration of contaminant particles and/or the largest acceptable diameter of contaminate particles allowable within the clean room.
Various measurement apparatuses have been developed to facilitate clean room management. A condensation particle counter, which is one such measurement apparatus, operates under the principle that the particle size increases during an alcohol evaporation process. An optical particle counter, which is another conventional measurement apparatus, measures the intensity of light scattered from a projected laser by the particles in the sampled air.
Examples of particle monitoring apparatuses including such particle counters are disclosed, for example, in Japanese Patent Application Publication No. 8-054265, Korean Patent No. 252215, and U.S. Pat. No. 5,856,623.
One conventional particle monitoring apparatus includes a sampling probe adapted to draw in an air sample, and a particle counter connected to the sampling probe. The sampling probe is connected to the particle counter by a sampling tube, and the vacuum pressure (i.e., a suction force) used to draw in the air sample in provided by a pump disposed within the particle counter. In the conventional particle monitoring apparatus, the flow rate of the air sample varies in accordance with the suction force applied by the pump, the length of the sampling tube, leakage of the air sample throughout the apparatus, etc.
However, variations in the air sample flow rate cause problems in the management of clean room cleanliness. For example, when the air sample flow rate falls abnormally low, the exact of contaminate particles in the air cannot be accurately measured. Contamination of workpieces may result.
Thus, there is a need for an improved particle monitoring apparatus that allows an air sample to be drawn into a particle counter at a constant flow rate. Such an apparatus will more readily facilitate acquisition and evaluation of the air sample.